KR101584227B1 - Lithium secondary battery - Google Patents

Abstract

A lithium secondary battery according to the present invention includes a cathode, an anode, a separator interposed between the cathode and the anode, and a non-aqueous electrolyte, wherein the cathode includes a cathode active material which is a manganese- The non-aqueous electrolyte includes an organic solvent, an electrolyte salt and an additive, and the additive includes BF ₄ ^- as an anion.
According to the present invention, in operation of a lithium secondary battery, by reducing the elution amount of manganese, a decrease in the output of the battery can be prevented, and excessive use of manganese, which is lower in value than cobalt or nickel, The manufacturing cost of the battery can be reduced, and degradation of LiPF ₆ , which may be contained in the electrolyte salt, is suppressed, so that degradation of the performance of the battery can be reduced.

Description

[0001] Lithium secondary battery [0002]

The present invention relates to a lithium secondary battery, and more particularly, to a lithium secondary battery including a salt containing BF ₄ ^- ion as an additive for a cathode active material containing excessive manganese and a nonaqueous electrolyte, To reduce the power output of the battery.

Recently, interest in energy storage technology is increasing. As the application fields of cell phones, camcorders, notebook PCs, and electric vehicles further expand, there is a growing demand for higher energy density of batteries used as power sources for such electronic devices. Lithium secondary batteries are the ones that can best meet these demands, and researches on them are actively under way.

However, such a lithium secondary battery has safety problems such as ignition and explosion when using an organic electrolytic solution, and it is disadvantageous in that it is difficult to manufacture. In particular, with the recent expansion of the application range of lithium secondary batteries, lithium secondary batteries have been used under various conditions and environments, and the demand for lithium secondary batteries of higher capacity has been gradually increasing. In order to provide a high capacity lithium secondary battery, the working range of the electrode is gradually expanding, and the movement to high voltage can benefit from the capacity but the safety problem is made more remarkable than before.

On the other hand, lithium cobalt composite oxide, lithium nickel composite oxide, lithium manganese composite oxide and the like are used as the cathode active material used for the lithium secondary battery. Among them, a lithium manganese composite oxide containing manganese, which is abundant in resources and low in value, This is receiving attention.

However, in the lithium secondary battery containing manganese, the manganese component eluted and eluted from the electrolyte is precipitated on the surface of the anode active material, for example, the carbon material, and the manganese precipitated on the surface of the anode active material is removed from the anode active material There is a problem that the resistance of the battery is increased to degenerate the battery by promoting the decomposition of the electrolyte in the anode active material by the reduction reaction by receiving electrons.

The precipitation of these manganese components is more severe when stored at high temperatures, which leads to an increase in the resistance of the battery. When a lithium secondary battery including manganese is used as a power source for an electric vehicle, such a problem causes serious deterioration of output, which is a major cause of hindering development of a high performance (high output) lithium secondary battery.

Conventional studies for preventing deterioration in the performance of lithium secondary batteries including manganese include a method of suppressing dissolution of the spinel structure and a method of using an electrolyte additive. However, it still does not completely inhibit dissolution, and the electrolytic solution itself deteriorates during storage at high temperature, resulting in deterioration of performance.

Therefore, there is a high need for a lithium secondary battery capable of solving the above problems.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a lithium secondary battery which does not cause a decrease in output of a battery by reducing the elution amount of manganese in operation of the lithium secondary battery.

According to the present invention, there is provided a lithium secondary battery comprising a cathode, an anode, a separator interposed between the cathode and the anode, and a non-aqueous electrolyte, wherein the cathode comprises a cathode active material, Wherein the non-aqueous electrolyte comprises an organic solvent, an electrolyte salt and an additive, wherein the additive comprises BF ₄ ^- as an anion.

Wherein the manganese-rich metal oxide is Li _x Mn _a M ¹ _b M ² _c M ³ _d O ₂ (0.5? A? 1, 0? B + c + d? 0.5, x + a + b + c + d _{= 2), Li y Mn e} M 1 f M 2 g M 3 h O 3 (0.5≤e≤1, 0≤f + g + h≤0.5, y + e + f + g + h = 3) , and Li _z Mn _i M ¹ _j M ² _k M ³ _l O ₄ ( ^1? _i? ² , 0? j + k + 1? 1, 2z + i + j + one or a mixture of two or more of these, wherein M ^1, M ² and M ³ are any one element of one another and independently selected from the group consisting of Al, Mg, Mn, Ni, Co, Cr, V and Fe .

At this time, the manganese-rich metal oxide may be a mixture of Li ₂ MnO ₃ and LiMn _{0 .5} Ni _{0 .5} O ₂ .

Examples of the organic solvent include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, (DEC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), dimethyl carbonate (DMF) Methyl ethyl ketone, ethyl propyl carbonate, dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, Propyl propionate,? -Butyrolactone,? -Valerolactone,? -Caprolactone,? -Valerolactone and? -Caprolactone Ton, or a mixture of two or more thereof.

Also, the organic solvent may include 60 to 80% by weight of any one selected from the group consisting of ethylmethyl carbonate, dimethyl carbonate, and diethyl carbonate, or a mixture of two or more thereof, and 20 to 40% by weight of ethylene carbonate. But is not limited thereto.

The electrolyte salt may be an anion selected from the group consisting of F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N (CN) ₂ ^- , ClO ₄ ^- , PF ₆ ^- , (CF ₃ ) ₂ PF ₄ ^- (CF ₃ ) ₃ PF ₃ ^- , (CF ₃ ) ₄ PF ₂ ^- , (CF ₃ ) ₅ PF ^- , (CF ₃ ) ₆ P ^- , CF ₃ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^{- _{3 SO 2) 2 N -,}} (FSO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, (CF 3 SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- , or two or more of them. The electrolyte salt may be LiPF ₆ .

On the other hand, the additive containing BF ₄ ^- as the anion is LiBF ₄ and R ₁ R ₂ R ₃ R ₄ NBF ₄ (R ₁ , R ₂ , R ₃ and R ₄ are each an alkyl group of C ₁ to C ₁₂ ) Or a mixture of two or more thereof.

The content of the additive may be 0.1 part by weight to 4 parts by weight based on 100 parts by weight of the organic solvent.

The nonaqueous electrolytic solution may be any one selected from the group consisting of vinylene carbonate, vinylethylene carbonate, cyclic sulfite, saturated sulphone, unsaturated sulphone, acyclic sulphone, and derivatives thereof, or a mixture of two or more thereof .

Meanwhile, the anode may include an anode active material including lithium metal, a carbon material, a metal compound, or a mixture thereof.

The metal compound may be at least one selected from the group consisting of Si, Ge, Sn, Pb, P, Sb, Bi, Al, Ga, In, Ti, Mn, Fe, Co, Ni, Cu, Zn, Ag, Or a compound containing two or more of these metal elements, or a mixture thereof.

The lithium secondary battery may be a cylindrical, square, pouch or coin-type battery.

According to the present invention, by reducing the elution amount of manganese, a lithium secondary battery that prevents the output of the battery from being lowered can be manufactured.

Further, by using manganese, which is lower in value than cobalt or nickel, as the cathode active material, the manufacturing cost of the lithium secondary battery can be reduced.

In addition, degradation of LiPF ₆ , which may be contained in the electrolyte salt, is suppressed, and deterioration of battery performance can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments of the invention and, together with the description of the invention, It should not be construed as limited.
1 is a graph showing life characteristics of a lithium secondary battery according to an embodiment of the present invention and a comparative example.
2 is a SEM photograph showing a surface and a cross section of a separation membrane according to an embodiment of the present invention.
3 is a SEM photograph showing a surface and a cross section of a separation membrane according to another embodiment of the present invention.
4 is a SEM photograph showing a surface and a cross section of a separation membrane according to a comparative example of the present invention.
5 is a SEM photograph showing a surface and a cross section of a separation membrane according to another comparative example of the present invention.

Hereinafter, the present invention will be described in detail. The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

In addition, since the embodiments described in the present specification and the configurations shown in the drawings are only the most preferred embodiments of the present invention and do not represent all the technical ideas of the present invention, It is to be understood that equivalents and modifications are possible.

According to the present invention, there is provided a lithium secondary battery including a cathode, an anode, a separator interposed between the cathode and the anode, and a non-aqueous electrolyte, wherein the cathode includes a cathode active material which is a manganese- , An organic solvent, an electrolyte salt, and an additive, wherein the additive comprises BF ₄ ^- as an anion.

When the additive contains BF ₄ ^- as an anion, it reacts with PF ₅ , which can be formed from an electrolyte salt, thereby suppressing the generation of PF ₅ having high reactivity while generating PF ₆ ^- , thereby lowering the reactivity of the non- Thereby contributing to the stabilization of the electrolytic solution and forming a surface protective coating of a stable inorganic layer such as LiF on the surface of the cathode to suppress further electrolyte reaction. Examples of the additive containing BF ₄ ^- as such an anion include LiBF ₄ , R ₁ R ₂ R ₃ R ₄ NBF ₄ (wherein R ₁ , R ₂ , R ₃ and R ₄ are each a C ₁ to C ₁₂ alkyl group) And preferably LiBF ₄ , (CH ₃ ) ₄ NBF ₄ , (C ₂ H ₅ ) ₄ NBF ₄ and the like can be used.

As the organic solvent, any of those commonly used in an electrolyte for a lithium secondary battery can be used without limitation. For example, ether, ester, amide, linear carbonate and cyclic carbonate may be used alone or in combination of two or more. have.

Among them, a carbonate compound which is typically a cyclic carbonate, a linear carbonate, or a mixture thereof may be included.

Specific examples of the cyclic carbonate compound include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, Propylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and halides thereof, or a mixture of two or more thereof. Examples of such halides include, but are not limited to, fluoroethylene carbonate (FEC) and the like.

Specific examples of the linear carbonate compound include any one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate and ethyl propyl carbonate And mixtures of two or more of them may be used as typical examples, but the present invention is not limited thereto.

Particularly, 60 wt% to 80 wt% of any one selected from the group consisting of ethylmethyl carbonate, dimethyl carbonate, and diethyl carbonate, which is a low viscosity, low dielectric constant linear carbonate, or a mixture of two or more thereof, When an organic solvent containing 20% by weight to 40% by weight of ethylene carbonate, which is a cyclic carbonate having a high viscosity in a carbonate-based organic solvent, is used, a non-aqueous electrolyte having a high electrical conductivity can be produced.

As the ether in the organic solvent, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether and ethyl propyl ether or a mixture of two or more thereof may be used , But is not limited thereto.

Examples of the ester in the organic solvent include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate,? -Butyrolactone,? -Valerolactone,? -Caprolactone,? -Valerolactone and? -Caprolactone, or a mixture of two or more thereof, but the present invention is not limited thereto.

Further, as the anion of the electrolyte salt is contained in the non-aqueous electrolyte according to an embodiment of the present ^{invention, F -, Cl -, Br} -, I -, NO 3 -, N (CN) 2 -, ClO 4 -, _{^{PF 6 -, (CF 3)}} 2 PF 4 -, (CF 3) 3 PF 3 -, (CF 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO _{^{3 -, CF 3 CF 2 SO}} 3 -, (CF 3 SO 2) 2 N -, (FSO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH - , (SF ₅ ) ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- . Wherein the electrolytic salt, non-limiting examples, LiCl, LiBr, LiI, LiClO 4, LiB 10 Cl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiAlCl 4, CH 3 SO 3 Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, chloroborane lithium, and lower aliphatic carboxylic acid lithium, but are not limited thereto.

The content of the additive including BF ₄ ^- as the anion may be 0.1 to 4 parts by weight, or 0.5 to 1 part by weight based on 100 parts by weight of the organic solvent. The amount of elution can be further reduced, and deterioration in the performance of the battery can be prevented more effectively.

The nonaqueous electrolytic solution further includes any one selected from the group consisting of vinylene carbonate, vinylethylene carbonate, cyclic sulfite, saturated sulphone, unsaturated sulphone, non-cyclic sulphone, and derivatives thereof or a mixture of two or more thereof can do. These compounds can serve to improve the characteristics of a protective layer (solid electrolyte interface, SEI) formed by the non-aqueous electrolyte reacting with the cathode active material and formed on the surface of the active material. In particular, they can be used together with an additive containing BF ₄ ^- It is possible to suppress the decomposition reaction at the surface of the electrolyte itself or at the surface of the cathode. Therefore, it is possible to suppress the elution of the metal ions from the cathode and suppress the side reaction of the electrolyte.

The content of these compounds may be 0.1 to 4 parts by weight based on 100 parts by weight of the organic solvent.

Examples of the cyclic sulfite include ethylene sulfite, methyl ethylene sulfite, ethyl ethylene sulfite, 4,5-dimethylethylene sulfite, 4,5-diethyl ethylene sulfite, propylene sulfite, Diethyl propyl sulfite, 4,6-diethyl propyl sulfite, and 1,3-butylene glycol sulfite. The saturated sulphone includes, for example, 1,3-propane sultone, and 1,4-butane sultone. Examples of the unsaturated sultone include ethene sultone, 1,3-propene sultone, 1,4-butene sultone, Phenolsaltone, and the like. Examples of the non-cyclic sulfone include divinyl sulfone, dimethyl sulfone, diethyl sulfone, methyl ethyl sulfone, and methyl vinyl sulfone.

Particularly, it may further comprise 0.5 to 4 parts by weight of vinylene carbonate (VC) or 0.5 to 3.5 parts by weight of 1,3-propane sultone (PS) based on 100 parts by weight of the nonaqueous electrolyte solution.

The lithium secondary battery according to an embodiment of the present invention can be manufactured according to a conventional method known in the art. For example, a porous separator may be inserted between the cathode and the anode, and the nonaqueous electrolyte solution according to the present invention may be added to the separator.

The separator used in one embodiment of the present invention may be any porous substrate commonly used in the art, and may be, for example, a polyolefin porous membrane or a nonwoven fabric, but is not particularly limited thereto .

Examples of the polyolefin-based porous film include polyolefin-based polymers such as polyethylene, polypropylene, polybutylene, and polypentene, such as high density polyethylene, linear low density polyethylene, low density polyethylene and ultra high molecular weight polyethylene, One membrane can be mentioned.

The nonwoven fabric may include, in addition to the polyolefin nonwoven fabric, for example, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate ), Polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylenesulfide, and polyethylene naphthalene, which may be used alone or in combination, And nonwoven fabrics formed by mixing these polymers. The structure of the nonwoven fabric may be a spun bond nonwoven fabric or a meltblown nonwoven fabric composed of long fibers.

The thickness of the porous substrate is not particularly limited, but may be 5 to 50 탆, and the pore size and porosity present in the porous substrate are also not particularly limited, but may be 0.01 to 50 탆 and 10 to 95%, respectively.

The anode has a structure in which the anode layer including the anode active material and the binder is supported on one or both surfaces of the current collector.

As the anode active material, a carbon material, a lithium metal, a metal compound, or a mixture thereof, in which lithium ions can be occluded and released, can be used.

Concretely, as the carbon material, low-crystallinity carbon and high-crystallinity carbon may be used. Examples of the low crystalline carbon include soft carbon and hard carbon. Examples of highly crystalline carbon include natural graphite, Kish graphite, pyrolytic carbon, liquid crystal pitch carbon fiber high temperature sintered carbon such as mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch derived cokes.

The metal compound may be at least one selected from the group consisting of Si, Ge, Sn, Pb, P, Sb, Bi, Al, Ga, In, Ti, Mn, Fe, Co, Ni, Cu, Zn, Ag, And compounds containing at least one metal element. These metal compounds may be a single substance, an alloy, an oxide (TiO ₂ , SnO ₂ Or the like), a nitride, a sulfide, a boride, an alloy with lithium, or the like, but an alloy with a single substance, an alloy, an oxide, and lithium can be increased in capacity. Among them, it may contain at least one element selected from Si, Ge and Sn, and it may further increase the capacity of the battery including at least one element selected from Si and Sn.

The cathode has a structure in which a cathode layer including a cathode active material, a conductive material and a binder is supported on one or both surfaces of the current collector.

As the cathode active material, a lithium-containing transition metal oxide may be used, and a manganese-rich metal oxide is included. Wherein the manganese-rich metal oxide is Li _x Mn _a M ¹ _b M ² _c M ³ _d O ₂ (0.5? A? 1, 0? B + c + d? 0.5, x + a + b + c + d = 2 ^{_{), Li y Mn e M 1}} f M 2 g M 3 h O 3 (0.5≤e≤1, 0≤f + g + h≤0.5, y + e + f + g + h = 3) and the Li _z Mn M ¹ M ² _{j i k l} M ³ O _4, or any one selected from the group consisting of (1≤i≤2, 0≤j + k + l≤1 , 2z + i + j + k + l = 4) and mixtures of two or more of the M ^1, M ² and M ³ are, may be any one of the elements to each other independently selected from the group consisting of Al, Mg, Mn, Ni, Co, Cr, V and Fe .

At this time, the manganese-rich metal oxides, Li ₂ MnO ₃ and LiMn _{0 .5 0 .5} O Ni may be a mixture of _2, wherein the Li ₂ MnO ₃ and LiMn _{0 .5} Ni _{0 .5} O ₂ is 1: 1 By weight based on the total weight of the composition.

The cathode active material may be coated with a metal such as aluminum (Al) or a metal oxide. In addition to the lithium-containing transition metal oxide, sulfide, selenide and halide may also be used.

The conductive material is not particularly limited as long as it is an electron conductive material that does not cause a chemical change in an electrochemical device. In general, carbon black, graphite, carbon fiber, carbon nanotube, metal powder, conductive metal oxide, organic conductive material and the like can be used. Commercially available products as the conductive material include acetylene black series (manufactured by Chevron Chemical Co., (Chevron Chemical Company or Gulf Oil Company products), Ketjen Black EC series (Armak Company), Vulcan XC-72 (Cabot Company) and Super P (MM (MMM)). For example, acetylene black, carbon black and graphite.

The cathode and the binder used for the anode have a function of holding the cathode active material and the anode active material in the current collector and also connecting the active materials, and commonly used binders can be used without limitation.

For example, it is possible to use vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, styrene Various types of binder polymers such as styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), and the like can be used.

The current collector used for the cathode and the anode may be any metal having a high conductivity and a metal which can easily adhere to the slurry of the active material and is not reactive in the voltage range of the battery. Specifically, examples of the current collector for a cathode include aluminum, nickel, or a combination thereof. Examples of the current collector for an anode include copper, gold, nickel, or a copper alloy or a combination thereof And the like. In addition, the current collector may be used by laminating the substrates made of the above materials.

The cathode and the anode are kneaded using an active material, a conductive material, a binder and a high boiling point solvent to prepare an electrode mixture, and then the mixture is coated on a copper foil or the like of the current collector, dried, Followed by heat treatment at a temperature of about 250 DEG C for about 2 hours under vacuum.

The outer shape of the lithium secondary battery according to an embodiment of the present invention is not particularly limited, but may be cylindrical, square, pouch type, coin type, or the like using a can.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Example  One

(1) Preparation of non-aqueous electrolyte

Ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 1: as the additive after the second manufacturing the organic solvent mixture in a weight ratio of LiBF ₄ is, LiPF ₆ as an electrolyte salt to 2 parts by weight based on 100 parts by weight of organic solvent part Was added so as to be 1 M to prepare a nonaqueous electrolytic solution.

(2) Manufacture of cathode

As a cathode active material, Li ₂ MnO ₃ and LiNi _{0 .5} Mn _{0 .5} O ₂ will mixed with the same weight ratio of the binder to Kureha KF-1100 (PVDF) 96 :: Super P as a conductive material in a weight ratio of 2:02 The mixture was mixed to prepare a slurry, coated on an aluminum (Al) foil current collector by a conventional method, and dried to prepare a cathode.

(3) Manufacture of anode

The anode active material slurry was prepared by mixing artificial graphite: SBR binder: carboxymethyl cellulose (CMC) as a thickener at a weight ratio of 98: 1: 1, and then coated on a collector of copper (Cu) foil by a conventional method, .

(4) Production of lithium secondary battery

A coin-shaped half-cell was fabricated by a conventional method using an electrode assembly manufactured by interposing a polyethylene porous film between the cathode and the anode.

Example  2

A coin-shaped half cell was prepared in the same manner as in Example 1, except that a non-aqueous electrolyte prepared by adding 1.5 parts by weight of 1,4-propane sultone was used in the preparation of the non-aqueous electrolyte.

Comparative Example  One

A coin-shaped half-cell was prepared in the same manner as in Example 1, except that a nonaqueous electrolytic solution prepared by adding 2 parts by weight of vinylene carbonate (VC) instead of LiBF ₄ as an additive in the preparation of the non-aqueous electrolyte was used.

Comparative Example  2

A nonaqueous electrolytic solution was prepared in the same manner as in Example 1 except that a nonaqueous electrolyte prepared by adding 2 parts by weight of vinylene carbonate (VC) and 1.5 parts by weight of 1,4-propane sultone instead of LiBF ₄ as an additive was used To prepare coin-shaped half cells.

Comparative Example  3

A coin-shaped half cell was prepared in the same manner as in Example 1, except that a non-aqueous electrolyte prepared by adding 1.5 parts by weight of 1,4-propane sultone instead of LiBF ₄ as an additive in the preparation of the non-aqueous electrolyte was used.

Comparative Example  4

A coin-shaped half-cell was prepared in the same manner as in Example 1, except that, in the preparation of the non-aqueous electrolyte, the non-aqueous electrolyte prepared by not adding LiBF ₄ was used.

Test Example  1: Evaluation of battery life characteristics

The half-cells prepared in Examples 1 and 2 and Comparative Examples 1 to 4 were subjected to a constant current charging up to 4.5 V at 0.5 C and a constant current discharge to 2.5 V at 0.5 C for 30 times, The measurement results are shown in Fig. The final life characteristics after 30 charge and discharge cycles are shown in Table 1 below. At this time, the final lifetime characteristics were indicated by the capacity retention rate after 30 cycles of charging / discharging with respect to the initial capacity.

Additive used Capacity retention rate (%) Example 1 LiBF ₄ 2 parts by weight 97.3 Example 2 LiBF ₄ 2 parts by weight + PS 1.5 parts by weight 96.4 Comparative Example 1 VC 2 parts by weight 95.3 Comparative Example 2 VC 2 parts by weight + PS 1.5 parts by weight 92.7 Comparative Example 3 PS 1.5 parts by weight 83.4 Comparative Example 4 none 91.4

As shown in Fig. 1 and Table 1, it can be seen that the embodiments according to the present invention have larger capacity retention ratios than the comparative examples.

Test Example  2 : Separator Minor reactant  Detection evaluation

After 30 charge / discharge cycles were completed, the surface and the cross-section of the separator were photographed by SEM, with respect to the half-cells prepared in Examples 1 and 2 and Comparative Examples 1 and 2.

2 and 3 are graphs showing the results of a comparison between a non-aqueous electrolyte (Example 1) to which LiBF ₄ was added as an additive, a nonaqueous electrolyte solution to which LiBF ₄ and PS were added (Example 2) 4 and 5 are graphs showing SEM photographs of each of the batteries after completion of the test. Figs. 4 and 5 are graphs showing the results of a comparison between the nonaqueous electrolyte solution (Comparative Example 1) in which VC is added as an additive and the nonaqueous electrolyte solution ), A separator SEM photograph of each of the batteries after 30 charge / discharge tests is shown.

2 to 5, when a compound containing BF ₄ ^- as an anion is added as an additive in the non-aqueous electrolyte, the amount of manganese-containing side reactants formed on the surface and the cross section of the separator I could confirm that it was small.

2 to 5 show the elution amounts of manganese formed after adding the cathode active material to each of the non-aqueous electrolytic solutions. As a result, it was confirmed that the elution amount of manganese in the nonaqueous electrolyte solution to which no compound containing BF ₄ ^- as an anion was added was large. The eluted manganese precipitates on the surface of the anode active material, and the precipitated manganese absorbs electrons from the anode active material to accelerate decomposition of the electrolyte by the reduction reaction, thereby increasing the resistance of the cell and degenerating the cell.

However, BF ₄ ^- in the non-aqueous electrolyte compound is added containing an anion to check that the elution of manganese with little, as an additive for non-aqueous electrolyte therefrom BF ₄ ^- the battery degradation by the addition of a compound comprising an anion It was found that there is an effect that can be prevented.

Claims (13)

A lithium secondary battery comprising a cathode, an anode, a separator interposed between the cathode and the anode, and a non-aqueous electrolyte,
Wherein the cathode comprises a cathode active material which is a manganese-rich metal oxide,
The nonaqueous electrolyte solution includes an organic solvent, an electrolyte salt, and an additive,
Wherein the additive comprises BF ₄ ^- as an anion,
Wherein the content of the additive is 0.1 part by weight to 4 parts by weight based on 100 parts by weight of the organic solvent. The method according to claim 1,
Wherein the manganese-rich metal oxide is Li _x Mn _a M ¹ _b M ² _c M ³ _d O ₂ (0.5? A? 1, 0? B + c + d? 0.5, x + a + b + c + d = 2 ^{_{), Li y Mn e M 1}} f M 2 g M 3 h O 3 (0.5≤e≤1, 0≤f + g + h≤0.5, y + e + f + g + h = 3) and the Li _z Mn M ¹ M ² _{j i k l} M ³ O _4, or any one selected from the group consisting of (1≤i≤2, 0≤j + k + l≤1 , 2z + i + j + k + l = 4) A mixture of two or more thereof,
Wherein each of M ¹ , M ² and M ³ is independently any one selected from the group consisting of Al, Mg, Mn, Ni, Co, Cr, V and Fe. 3. The method of claim 2,
Wherein the manganese-rich metal oxide is a mixture of Li ₂ MnO ₃ and LiMn _{0 .5} Ni _{0 .5} O ₂ . The method according to claim 1,
Examples of the organic solvent include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, (DEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate A solvent such as methanol, ethanol, propanol, isopropanol, isopropanol, butanol, isopropanol, butanol, isopropanol, Pyronate,? -Butyrolactone,? -Valerolactone,? -Caprolactone,? -Valerolactone and? -Caprolactone Luer binary group either or lithium secondary battery, characterized in that a mixture of two or more of those selected from the. The method according to claim 1,
Wherein the organic solvent comprises 60 wt% to 80 wt% of any one selected from the group consisting of ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate, or a mixture of two or more thereof, and 20 wt% to 40 wt% Lt; RTI ID = 0.0 > rechargeable < / RTI > The method according to claim 1,
The electrolytic salt is preferably an anion selected from the group consisting of F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N (CN) ₂ ^- , ClO ₄ ^- , PF ₆ ^- , (CF ₃ ) ₂ PF ₄ ^{- _{3) 3 PF 3 -, (}} CF 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO ^{_{2) 2 N -, (FSO}} 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, (CF 3 SO 2) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- , or two or more of them. The method according to claim 1,
Wherein the electrolyte salt is LiPF ₆ . The method according to claim 1,
The additive comprising BF ₄ ^- as the anion is selected from the group consisting of LiBF ₄ , R ₁ R ₂ R ₃ R ₄ NBF ₄ (R ₁ , R ₂ , R ₃ and R ₄ are each an alkyl group of C ₁ to C ₁₂ ) , Or a mixture of two or more thereof. delete The method according to claim 1,
The nonaqueous electrolytic solution further includes any one selected from the group consisting of vinylene carbonate, vinylethylene carbonate, cyclic sulfite, saturated sulphone, unsaturated sulphone, non-cyclic sulphone, and derivatives thereof or a mixture of two or more thereof Lt; RTI ID = 0.0 > rechargeable < / RTI > The method according to claim 1,
Wherein the anode comprises an anode active material comprising a lithium metal, a carbon material, a metal compound, or a mixture thereof. 12. The method of claim 11,
The metal compound may be at least one selected from the group consisting of Si, Ge, Sn, Pb, P, Sb, Bi, Al, Ga, In, Ti, Mn, Fe, Co, Ni, Cu, Zn, Ag, Or a compound containing two or more of these metal elements, or a mixture thereof. The method according to claim 1,
Wherein the lithium secondary battery is a cylindrical, square, pouch-type, or coin-type battery.

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